Optimization For Lowest Carry-Over; Using The Automated Needle Wash - Agilent Technologies G1367A Reference Manual

Optimization for Lowest Carry-over

Several parts of an injection system can contribute to carry-over:
• needle outside
• needle inside
• needle seat
• sample loop
• seat capillary
• injection valve
The well plate sampler continuous flow-through design ensures that sample
loop, needle inside, seat capillary, and the mainpass of the injection valve is
always in the flow line. These parts are continuously flushed during an
isocratic and also during a gradient analysis. The residual amount of sample
remaining on the outside of the needle after injection may contribute to
carry-over in some instances. When using small injection volumes or when
injecting samples of low concentration immediately after samples of high
concentration, carry-over may become noticeable. Cleaning the needle in the
flush port or using the automated needle wash enables the carry-over to be
minimized and prevents also contamination of the needle seat.

Using the Automated Needle Wash

The automated needle wash can be programmed either as "injection with
needle wash" or the needle wash can be included into the injector program.
When the automated needle wash is used, the needle is moved into a wash vial
after the sample is drawn. By washing the needle after drawing a sample, the
sample is removed from the surface of the needle immediately.
Uncapped Wash Vial
For best results, the wash vial should contain solvent in which the sample
components are soluble, and the vial should not be capped. If the wash vial is
capped, small amounts of sample remain on the surface of the septum, which
may be carried on the needle to the next sample.
1100 Series WS MWS Reference Manual
Optimizing Performance
2
45